The invention relates to an antenna for the reception of circularly polarized satellite radio signals.
Particularly in the case of satellite radio systems, what is particularly important is the efficiency of the transmission output emitted by the satellite, and the efficiency of the reception antenna. Satellite radio signals are generally transmitted with circularly polarized electromagnetic waves, because of polarization rotations on the transmission path. In many cases, program contents are transmitted on separate frequency bands that lie close to one another in frequency. This is done, using the example of SDARS satellite radio, at a frequency of approximately 2.3 GHz, in two adjacent frequency bands, each having a bandwidth of 4 MHz, at a distance between the center frequencies of 8 MHz and 4 MHz, respectively. The signals are emitted by different satellites, with an electromagnetic wave that is circularly polarized in one direction. Accordingly, circularly polarized antennas are used for reception in the corresponding direction. Such antennas are known, for example, from DE-A-4008505 and DE-A-10163793. This satellite radio system is additionally supported by means of the transmission of terrestrial signals, in certain areas, in another frequency band having the same bandwidth, disposed between the two satellite signals.
In the case of a satellite radio system in which signals in frequency bands that lie close to one another. in frequency, and have approximately the same width, but the circularly polarized waves must be emitted in opposite directions of rotation. These differently circularly polarized antennas would accordingly have to be used for the reception of the two frequency bands, for example, according to the patterns of the embodiments known from DE-A-4008505 and DE-A-10163793. For reception in vehicles, in particular, the use of multiple antennas having separate lines to the receiver, i.e. the use of a complicated switching device for selective reception of the one or the other signal, is economically complicated and therefore disadvantageous. Separate processing of the two frequency bands, using frequency-selective measures, within one and the same antenna, cannot be achieved with efficient means, because of the great selection requirement.